Thermal Evolution of Three Selected Preceramic POSSs Into Ceramic Materials

Three polyhedral oligomeric silsesquioxanes (POSSs), OctaTetraMethylAmmonium-POSS (OTMAP), DodecaPhenyl-POSS (DPP), and OctaMethyl-POSS (OMP) were heated to explore their potential as preceramic POSSs for ceramic materials, under a three-step pyrolysis technique (25–500 °C/4 h, 500–1000 °C/6 h and 1000–1500 °C/8 h, 10 °C/min in N₂). The chemical and structural evolutions were carefully characterized by TG-DTA, XRD, FTIR and SEM. The OTMAP system was crystalline at all steps, and was mostly transformed into cristobalite at 1500 °C. While, the other two systems produced amorphous silica-based phases (ASBPs) in the first and second steps. In the third step, the DPP with Si–C and Si–O bonds was transformed into crystalline SiC and ASBPs, and OMP with Si–C and Si–O bonds was converted to only ASBPs. Such different transformations between DPP and OMP could be ascribed to their distinct original molecular structures and POSS-dependent chemical evolution.